JP2007135948A - Magnetic resonance imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the noise of a magnetic resonance imaging apparatus by preventing the transmission of the vibration of a gradient magnetic field coil to an exterior cover of a scanner gantry. <P>SOLUTION: This magnetic resonance imaging apparatus is provided with a static magnetic field generating means 1 generating an almost uniform static magnetic field, the gradient magnetic field coil 2 disposed in a static magnetic field region by the static magnetic field generating means 1 and generating a gradient magnetic field, an irradiation coil 3 irradiating high frequency signals to a subject, a receiving coil 4 receiving nuclear magnetic resonance signals from the subject, the scanner gantry consisting of the elements and the exterior cover 8 covering the scanner gantry; and a reinforcing member 9 is provided between the exterior cover 8 and the static magnetic field generating means 1 to support the exterior cover 8 and the static magnetic field generating means 1 in non-contact therewith. The exterior cover 8 comprises partial covers divided into a plurality of sections and is constituted of joining the partial covers, and the joints of the partial covers are filled with silicone rubber or packing materials to completely seal the static magnetic field generating means 1 and the gradient magnetic field coil 2. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a magnetic resonance imaging apparatus, and more particularly to a magnetic resonance imaging apparatus capable of reducing noise generated by vibration of a gradient magnetic field coil.

  A magnetic resonance imaging device uses a nuclear magnetic resonance phenomenon of a nucleus to obtain a magnetic resonance image that represents the physical properties of an object placed in the imaging space, and generates a static magnetic field that generates a static magnetic field in the imaging space. Means, a gradient magnetic field generating means for giving a linear gradient magnetic field superimposed on the static magnetic field, an irradiation coil for generating high-frequency electromagnetic waves for causing nuclear magnetic resonance in the atomic nuclei constituting the subject, and the nucleus A receiving coil for detecting an echo signal generated by magnetic resonance is provided, and an image is reconstructed using the echo signal to obtain a tomographic image.

In such a magnetic resonance imaging apparatus, in recent years, there is a growing need for shortening the time required for imaging.
In response to this requirement, a pulse sequence with high-speed reversal of gradient magnetic field pulses has been developed and put into practical use to support single-shot or multi-shot EPI (echo planar imaging), which is an ultra-high-speed imaging technique. Yes.

When capturing an image using such a pulse sequence, a pulsed large current is passed through a gradient magnetic field coil placed in a static magnetic field in order to give positional information to each signal emitted from a measurement target. Lorentz force acts on the gradient coil to cause mechanical distortion in the gradient coil.
Since this phenomenon works repeatedly, the gradient coil vibrates and generates a large noise. Further, when the gradient magnetic field pulse is reversed at a high speed, the vibration increases, so that the noise increases as the imaging speed increases. To do.
This noise gives a very discomfort and anxiety to the subject placed in the imaging space, and techniques for reducing this noise are disclosed in Patent Document 1 and Patent Document 2.

  Patent Document 1 discloses that a gradient magnetic field coil is enclosed in a sealed space surrounded by a sound insulation cover and a static magnetic field generation source, and a sound wave generated by the gradient magnetic field coil is attenuated in a member constituting the sealed space to Attenuating the sound wave radiated to the noise reduces the noise.

Patent Document 2 discloses an entire gradient magnetic field coil including an intermediate member provided between the gradient magnetic field coil and a shield coil for shielding a magnetic field generated on the opposite side of the uniform magnetic field region of the coil. The intermediate part is fixed to the static magnetic field generating means via a vibration damping material, and the vibration of the gradient magnetic field coil is absorbed and attenuated by the vibration damping material to reduce vibration and noise. To do.
JP 2001-299719 A JP 2001-149338 JP

  In general, since the gradient magnetic field coil is fixed to the static magnetic field generating means by a bolt or the like, the vibration generated by the gradient magnetic field coil is transmitted to the static magnetic field generating means from the fixed point or contact point, and the static magnetic field generation The surface of the means becomes a noise radiation surface. For this reason, in the sound insulation structure according to Patent Document 1, the vibration of the gradient magnetic field coil is transmitted to the static magnetic field generating means, and the noise in the imaging space is not only the gradient magnetic field coil but also the static magnetic field generating means serves as a sound source. It is difficult to sufficiently reduce the noise. That is, the sound insulation structure according to Patent Document 1 cannot provide a sufficient noise reduction effect.

  Further, Patent Document 2 does not reduce the vibration of the gradient magnetic field coil itself, but reduces the vibration transmitted from the gradient magnetic field coil to the static magnetic field generating means by the vibration damping material. It is difficult to sufficiently reduce noise in the imaging space.

As described above, any of the above-described techniques reduces the vibration transmitted from the gradient magnetic field coil to the static magnetic field generating means to reduce noise, but these techniques alone are insufficient.
That is, the vibration of the gradient magnetic field coil is transmitted to the exterior cover of the scanner gantry via the static magnetic field generation source, and the exterior cover also vibrates, and this vibration also serves as a noise source to increase the noise of the entire apparatus. This is a factor, but this is not mentioned in Patent Documents 1 and 2 above.

  The present invention has been made in view of the above circumstances, and an object thereof is to reduce the noise of the magnetic resonance imaging apparatus by preventing the vibration of the gradient magnetic field coil from being transmitted to the exterior cover of the scanner gantry. For the purpose.

  The present invention has a structure in which the exterior cover of the scanner gantry is made in non-contact with the static magnetic field generating means and the gradient magnetic field generating means, so that vibrations generated by the gradient magnetic field coil as the gradient magnetic field generating means are not transmitted to the exterior cover. Thus, the noise is reduced. Specifically, this is achieved by the following means.

(1) Static magnetic field generating means for generating a substantially uniform static magnetic field, a gradient magnetic field coil for generating a gradient magnetic field arranged in a static magnetic field region by the static magnetic field generating means, and irradiation for irradiating a subject with a high frequency signal In the magnetic resonance imaging apparatus, comprising: a coil; a receiving coil that receives a nuclear magnetic resonance signal from the subject; a scanner gantry including the elements; and an exterior cover that covers the scanner gantry. Non-contact support means for supporting the cover in a non-contact manner from the static magnetic field generating means is provided.
(2) The non-contact support means includes a reinforcing member provided between the exterior cover and the static magnetic field generating means, and the reinforcing cover supports the external cover in a non-contact manner from the static magnetic field generating means.
(3) In the reinforcing member, a part facing the imaging space in the static magnetic field region by the static magnetic field generating means is made of a nonmagnetic and nonconductive material, and the other part is made of a nonmagnetic metal material.
(4) Fiber reinforced resin is used for the nonmagnetic and nonconductive material, and stainless steel is used for the nonmagnetic metal material.

In the scanner gantry configured in this way, the exterior cover and the static magnetic field generating means are supported in a non-contact manner by the reinforcing member, so that vibration from the gradient magnetic field coil is not transmitted to the exterior cover, The vibration of the outer cover is suppressed and noise is reduced.
Further, a non-magnetic and non-conductive material made of fiber reinforced resin is used for a portion facing the imaging space in the static magnetic field region of the reinforcing member, and stainless steel is used for a portion other than the portion facing the imaging space. Since a magnetic metal material is used, non-contact support means using a reinforcing member having an appropriate strength and not affected by magnetism can be provided.

  (5) The exterior cover is composed of partial covers divided into a plurality of parts. These partial covers are joined together, and silicon rubber or a packing material is filled in the joint between the partial covers.

In this way, by dividing the outer cover into a plurality of parts and filling the joint between the divided partial covers with silicon rubber or packing material, the static magnetic field generating means and the gradient magnetic field coil are completely sealed, Noise generated from the gradient coil can be insulated.
Further, by dividing the exterior cover into a plurality of parts, it is possible to improve the workability of attaching the exterior cover during installation or maintenance.

(6) The external sound of the exterior cover is covered with a sound absorbing material made of glass wool or urethane to reduce the echo sound to the outside.
(7) Further, a space between the outer cover and the static magnetic field generation source is vacuumed or a low density gas is sealed in the space to obtain a further noise reduction effect.

According to the present invention, since the static magnetic field generating means and the gradient magnetic field coil are hermetically sealed without contact with the exterior cover, the vibration of the gradient magnetic field coil is not transmitted to the exterior cover and noise in the imaging space is obtained. Can be reduced.
In addition, since the outer surface of the exterior cover is covered with the sound absorbing material, the external reverberation sound is reduced and a further noise reduction effect is obtained.

Hereinafter, embodiments of a magnetic resonance imaging apparatus according to the present invention will be described in detail with reference to the drawings.
The present invention relates to the structure of a scanner gantry that reduces noise by preventing the vibration of the gradient magnetic field coil from being transmitted to the exterior cover of the scanner gantry. It is common to both the electric magnet method and the permanent magnet method, and the magnetic field method in which the static magnetic field direction is either the vertical direction or the horizontal direction. The case where it applies to is demonstrated as an example.

FIG. 1 is a configuration diagram of a super-electric vertical magnetic field type open magnetic resonance imaging apparatus to which the sound insulation technique of the present invention is applied.
The open type is a magnetic resonance imaging device of a scanner gantry with a magnetic circuit in which a predetermined part of the measurement space is open. It provides a sense of openness for the subject, and the operator approaches the subject. It has a feature that it is easy to be damaged

  In FIG. 1, a magnetic resonance imaging apparatus generates a static magnetic field generating means 1 that generates a uniform static magnetic field in a direction perpendicular to the body axis of a subject, and a gradient magnetic field disposed inside the static magnetic field generating means 1 A gradient coil 2 for irradiating, an irradiation coil 3 for irradiating a high-frequency signal for causing nuclear magnetic resonance in an atomic nucleus constituting a living tissue of the subject, and a signal for receiving a signal emitted from the subject The receiving coil 4 constitutes a scanner gantry, and this scanner gantry is covered with an exterior cover (not shown).

  A high-frequency signal is transmitted to the irradiation coil 3 from a transmission system including a high-frequency transmitter and a modulator (not shown), a high-frequency amplifier, and the like, and an echo signal (NMR signal) of the subject by the transmitted high-frequency signal is transmitted. Detected by the receiving system by the receiving coil 4, the detected echo signal is converted into a digital quantity by an A / D (analog / digital) converter via an amplifier and a quadrature detector (not shown), and this conversion is performed. A digital signal is processed by a signal processing system.

  The signal processing system is an image obtained from an echo signal detected by the reception system by the image reconstruction calculation means 6 configured by a central processing unit (CPU), a calculation device, a storage device using a magnetic disk and a magneto-optical disk, and the like. The data is subjected to correction processing and various types of image processing to reconstruct an image, and the reconstructed tomographic image of an arbitrary cross section is displayed on the display means 7 using a display such as a CRT.

  The display means 7 includes external input means such as a keyboard and a mouse for setting an imaging sequence, parameters necessary for imaging, and inspection conditions such as an imaging section, and the respective elements are controlled by control means (not shown). Is done.

  The magnetic resonance imaging apparatus configured as described above positions the subject placed on the bed 5 at the imaging region, sets the inspection conditions, images based on the inspection conditions, and receives the receiving coil 4 The MRI image reconstructed using the nuclear magnetic resonance signal received in step 1 is displayed on the display means 7 for diagnosis.

The scanner gantry using the sound insulation structure, which is the main part of the present invention, will be described in the magnetic resonance imaging apparatus configured as described above.
FIG. 2 shows the positional relationship between the static magnetic field generating means 1 and the outer cover 8 using the reinforcing member 9 so that the static magnetic field generating means 1 and the outer cover 8 are not in contact with each other around the static magnetic field generating means 1. FIG.

In FIG. 2, the shaded portion is the static magnetic field generating means 1, the gradient magnetic field coil 2 is disposed inside the static magnetic field generating means 1, and the exterior cover 8 and the static magnetic field generating means 1 are in contact with each other. It is supported by the reinforcing member 9 so as not to occur.
The reinforcing member 9 has the outer cover 8 mounted on the reinforcing member 9, completely covering the first stage of the static magnetic field generating hand and the gradient magnetic field coil 2, and insulating the sound generated therefrom, and the outer cover 8 It is also a means to support.

The reinforcing member 9 uses a fiber reinforced resin such as glass epoxy in order to make the part facing the imaging space of the reinforcing member 9 nonmagnetic and nonconductive, and the other part is made of a nonmagnetic material or stainless steel. Any non-magnetic metal may be used.
Further, since the bed 5 is supported by the reinforcing member 9, the reinforcing member 9 needs to have a strength sufficient to support the bed 5.

The exterior cover 8 is composed of a plurality of partial covers for facilitating the attachment to the scanner gantry, and these partial covers are joined together to constitute the exterior cover 8.
In order to fill the gap of the joint of the partial cover configured as described above, the gap is filled with silicon rubber, packing, or the like.

  By adopting such a structure, not only the gradient magnetic field coil 2 but also the static magnetic field generating means 1 is completely sealed in the reinforcing member 9, and the vibration of the gradient magnetic field coil 2 is transmitted to the exterior cover 8. As a result, the noise caused by the vibration of the outer cover 8 caused by the vibration of the gradient magnetic field coil 2 is reduced, and the sound insulation by the outer cover 8 is further improved.

The sound insulation effect by the exterior cover 8 is determined by the mass rule shown in the equation (1) disclosed in Japanese Patent Laid-Open No. 2001-299719.
TL = 18 × log (f × ρ × t) −44 [dB] (1)
Here, TL is a transmission loss representing a sound insulation effect, f is a sound frequency, ρ is a density of the sound insulation material, and t is a thickness of the sound insulation material.
The above equation means that the sound insulation performance increases as the mass of the sound insulation material increases. To enhance the sound insulation effect, the outer cover 8 should be made of a material with a high density ρ and the thickness t should be increased. Is desirable.
Therefore, in order to enhance the sound insulation effect by the exterior cover 8 as a sound insulation material, a material having a high density ρ, for example, a material such as a fiber reinforced resin, is used, and the thickness t should be increased to such an extent that the workability is not impaired. .

  Furthermore, as shown in FIG. 3, the outer surface of the exterior cover 8 is covered with a sound absorbing material 10 made of glass wool or urethane, so that the noise in the imaging space is further reduced because the acoustic noise in the imaging space is reduced. It becomes.

  Note that the noise reduction effect is further improved by vacuuming the space between the exterior cover 8 and the static magnetic field generating means 1 or by enclosing a low density gas in the space.

1 is a configuration diagram of a super-electric vertical magnetic field type open type magnetic resonance imaging apparatus to which a sound insulation technique of the present invention is applied. FIG. The front view which shows the positional relationship of the static magnetic field generation means and exterior cover which support a static magnetic field generation means and an exterior cover by a reinforcement member non-contactingly. The figure which shows the structure which covers the outer surface of an exterior cover with a sound-absorbing material.

Explanation of symbols

  1 Static magnetic field generation means, 2 gradient coil, 3 irradiation coil, 4 receiving coil, 5 patient bed, 6 image reconstruction calculation means, 7 display means, 8 exterior cover, 9 reinforcing member, 10 sound absorbing material

Claims (7)

  A static magnetic field generating means for generating a substantially uniform static magnetic field, a gradient magnetic field coil for generating a gradient magnetic field arranged in a static magnetic field region by the static magnetic field generating means, an irradiation coil for irradiating a subject with a high frequency signal, A magnetic resonance imaging apparatus comprising: a receiving coil that receives a nuclear magnetic resonance signal from the subject; a scanner gantry including the elements; and an exterior cover that covers the scanner gantry. A magnetic resonance imaging apparatus comprising non-contact support means for non-contact support from a static magnetic field generation means.   The non-contact support means comprises a reinforcing member provided between the exterior cover and the static magnetic field generation means, and the reinforcement cover supports the external cover in a non-contact manner from the static magnetic field generation means. The magnetic resonance imaging apparatus according to claim 1.   The reinforcing member is characterized in that a portion facing the imaging space in the static magnetic field region by the static magnetic field generating means is made of a nonmagnetic and nonconductive material, and other portions are made of a nonmagnetic metal material. The magnetic resonance imaging apparatus according to claim 2.   4. The magnetic resonance imaging apparatus according to claim 3, wherein a fiber reinforced resin is used for the nonmagnetic and nonconductive material, and stainless steel is used for the nonmagnetic metal material.   The said exterior cover consists of a partial cover divided | segmented into plurality, These partial covers are joined together, The silicone rubber or packing material is filled into the joint of these partial covers, The any one of Claim 1 thru | or 4 characterized by the above-mentioned. 2. A magnetic resonance imaging apparatus according to claim 1.   6. The magnetic resonance imaging apparatus according to claim 1, wherein an outer surface of the outer cover is covered with a sound absorbing material made of glass wool or urethane.   The magnetic resonance imaging apparatus according to any one of claims 1 to 6, wherein a space between the outer cover and the static magnetic field generation source is vacuumed or a low-density gas is sealed in the space. .

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